doubt
1.I have no doubt that he will come soon和I have no doubt he will come soon都可以说。
2.可以说There is no doubt that he will come soon，不可说It is no doubt that he will come soon。
There is no doubt about it that he will come soon. =There is no doubt that he will come soon.
3.doubt（动词）除了在否定句和疑问句里以外，后面通常接whether而不接that，如通常说I do not doubt that he will come soon和Do you doubt that he will come soon? 但不说I doubt that he will come soon。最好把that改作whether。doubt用作名词也有这区别，如通常说There is no doubt that he will come soon和Is there any doubt that he will come soon? 但不说There is some doubt that he will come soon。最好把that改作whether。
4.在上面说过，I doubt that he will come soon里的that最好改作whether。用了that，不但不合习惯，而且往往有可能被人误解，因为在旧式些的英语里doubt that...作“恐怕…”或“料想…”解。
5.I doubt whether he will come soon含有“我想他不会不久就来”的意思，I doubt whether he will not come soon含有“我想他不久就来”的意思。
6.no doubt是状语短语，现在作“当然”或“大约”解，没有“确实无疑”那样的坚信的意思，如No doubt he meant well enough和You have no doubt heard of her before。要表示“确实无疑”的意思，该用undoubtedly，without doubt，without a doubt，beyond doubt或beyond a doubt。
7.in doubt有时作“怀疑的”解，有时作“使人怀疑的”解，如I am in doubt about his age和His age is in doubt。在用作“怀疑的”解的时候，后面往往不用介词而直接以what，where，how等开首的短语或从句。例如：
- I am in doubt what to do with it.
- I am in doubt where he lives.
- I am in doubt how to proceed.
8.I have no doubt about it和There is no doubt about it等句子里用单数形式doubt，但I have doubts about it里必须用复数形式。
